The present invention relates generally to servo-controlled actuators, and more specifically to a lens actuator which is servo-controlled to keep the optical axis of a tracking following device on the right track of a recording disk such as optical disks.
Conventional track following devices include a permanent magnet mounted on a base, and at least one pair of tracking coils and a focusing coil which are mounted on a resiliently movable support. These coils cooperate with the magnet to produce force components in a direction transverse to the direction of tracks to keep the optical axis of a lens system on a desired track and in an orthogonal direction to focus a light beam on the track. Magnetic flux density distribution generated by the permanent magnet has only one peak. As the tracking coils are moved in a focusing direction, flux densities at the upper and lower portions of the tracking coils tend to differ from each other, causing a rotary moment to occur in the movable support. The optical axis of the lens is thus tilted with respect to the vertical.